FIG. 1 illustrates the structure of an LTE downlink frame.
Referring to FIG. 1, a basic frame structure is based on the LTE frame structure illustrated in FIG. 1. In the frame structure, a Physical Downlink Control Channel (PDCCH) area for carrying a control signal is time-division-multiplexed with a Physical Downlink Shared Channel (PDSCH) for carrying data in every subframe. When an enhanced Node B (eNB) transmits signals on a downlink, PDCCH transmission precedes PDSCH transmission. The PDCCH delivers information about the PDSCH. User Equipments (UEs) may be aware of the transmission areas and Modulation and Coding Scheme (MCS) levels of data directed to them only by decoding PDCCHs. The eNB transmits information about data for a plurality of UEs using their Identifiers (IDs) on the PDCCHs. Apparently, the UEs also decode the PDCCHs using their IDs.
In a cellular system where a single eNB controls a plurality of UEs, the eNB controls them by transmitting control information on a downlink control channel. Due to a limit on the number of PDCCHs that the eNB may transmit at one time instant, the eNB transmits control information to a UE on an arbitrary PDCCH at each time instant, rather than a different PDCCH is allocated beforehand to each UE. The UE identifies control information for it on the PDCCH by its ID. At each time instant, the UE decodes a plurality of PDCCHs (or a plurality of available PDCCH formats) and if there is any PDCCH directed for it, the UE receives control information on the PDCCH and operates based on the control information.
For the most part, RNs are used to increase user throughput and extend service coverage. As RNs are differently implemented depending on system types, application environments, and purposes, many modifications have been proposed in relation to RNs.